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Prostate cancer is at the present time the most common form of cancer among men. The prostate is a walnut-sized gland in men that produces fluid that is a component in semen. The prostate has two, or more, lobes, or sections, enclosed by an outer layer of tissue. The prostate is located in front of the rectum and just below the urine bladder, and surrounds the urethra.
The occurrence of prostate cancer is highest in the northwestern part of Europe and in the United States. The growth of the tumor is usually a process that takes place during a long period of time. Prostate cancer is normally a mild form of cancer. In fact, the majority of men diagnosed with prostate cancer do survive, and only a minority of the men encounters a more aggressive form of prostate cancer, which metastasizes in an early stage. This form of prostate cancer may only be curable if it is diagnosed in an early stage, before the cancer has spread to extracapsular tissue.
Today diagnosis and monitoring of prostate cancer may be performed by measuring the concentration of a prostate specific antigen (PSA) in the blood of the patient. If the concentration of PSA is markedly high in several consecutive measurements, performed at different points of time, the assessment is that there is a probability of prostate cancer. At this point of time a biopsy may be performed to verify prostate cancer.
PSA (also known as kallikrein III) is a protein, constituted of a single chain of 237 amino acids, that is produced in the secretory cells of the prostate. These secretory cells may be found in the whole prostate gland. PSA is well established and thoroughly researched marker in respect of prostate cancer. By comparison with healthy cells the production of PSA is lower in malignant cells and higher in hyperplastic cells. It is therefore contradicting that in fact the concentration of PSA is higher in blood from men suffering from prostate cancer. However, one explanation may be that the malignant cells have a deteriorated cell structure, and are therefore more permeable to PSA.
Another important serine protease, which may be suitable for future therapy of prostate cancer, is human glandular kallikrein 2 (hK2). The gene coding hK2 is located on chromosome 19, together with the gene coding for PSA. hK2 is expressed mainly in the prostate tissue, just as PSA. In the prostate, PSA is present as an inactive pro-form and is activated through the peptidase action of hK2. Immunohistochemical research in respect of hK2 has shown that hK2 is expressed in relation to the level of differentiation. This means that hK2 is expressed in a higher yield in tissue of low differentiation, such as tissue subjected to prostate cancer, and in a lower yield in tissue of high differentiation, such as tissue subjected to benign prostatic hyperplasia (BPH) which is another common prostate problem.
Today's therapies of prostate cancer are surgery (e.g., radical prostatectomy), radiation therapy (including, brachytherapy and external beam radiation therapy, high-intensity focused ultrasound (HIFU), chemotherapy, oral chemotherapeutic drugs, cryosurgery (freezing the tumor), hormonal therapy (such as antiandrogen therapy), castration or combinations of the foregoing.
Most of these therapies (surgery and external radiation therapy) are, however, only (or primarily) useful for treatment of primary tumors and large metastases. Chemotherapy is used for disseminated of the cancer but for most of these patients, it is a palliative effect and/or prolonged survival. Other or complementary treatment modalities are therefore necessary to achieve considerable improvements of the disseminated malignant diseases, particular in cases of micrometastases.
Therapy, such as immunotherapy or radioimmunotherapy, using targeting molecules such as antibodies and fragments could give the possibility of therapy of disseminated disease.
Thus, there is a need for a new therapeutic agents and methods for treating prostate cancer, particular in cases of disseminated disease, metastases and micrometastases.